Axial external fixation devices of reduced dimensions are known such as, for example, the axial external fixation device Model No. 30,000 produced and marketed by applicants' assignee and described and claimed in European Patent No. 11,258 and in U.S. Pat. No. 4,621,627.
Such known fixation devices are generally formed of an extendable central body. The longitudinal ends of the central body are connected to clamps for bone pins or screws, and each of the end connections is via a universal joint which can be releasably locked in a predetermined orientation of the clamp to the central body.
Each universal joint comprises a ball which is integral with a clamp. The rest of the joint is a socket formation at an end of the central body, and a sleeve carried by the body end captively retains the ball. An eccentric is also carried by the body end and is rotatable to selectively and releasably lock the captive orientation of the ball and thus the clamp with respect to the body. The eccentric is externally accessible for rotation by a suitable tool.
The central body is formed of two or more telescopically movable elements which can be locked in desired position by suitable locking members.
The model of the fixation device described above is produced in several sizes, one of which is intended for the reduction and stabilizing of fractures of children and of the smaller bones of adults, for example, of the wrist or ankle.
However, even this type of fixation device has several known drawbacks, among which, in particular, is the opacity of the central body to X-rays. Such opacity prevents multilateral radioscopy of fractures during a reduction and in the course of subsequent check-ups.
Another drawback of the known fixation devices resides in the large amount of space they require due to the fact that sleeves and eccentric locking devices are arranged between the central body and the respective clamps, thus accounting for an overall fixation-device length which limits the minimum distance between clamped sets of bone screws, thereby limiting the range of central-body adjustment, for a given overall fixator length.
Another drawback resides in the relatively great weight of the traditional fixation devices, particularly for the treatment of wrist fractures and in general of children and the elderly.
Another drawback of existing devices wherein the telescoping body parts are cylindrical, and therefore twistable unless locked, is that they have no means to adapt a given patient's installation to limited dynamization of the externally fixated stumps of the fracture, whereby to accelerate remarginization of the fracture.